Photoflash lamp and ignition means therefor



Nov. 19, 1963 w. c. FINK ETAL PHOTOFLASH LAMP AND IGNITION MEANS THEREFOR Filed Dec. 1. 1960 WILLIAM C. FINK MAGNUS NORDSTROM INVENTOR.

ATTORNE II? I a United States Patent Oflfice 3,1 1 L016 Patented Nov. 19, 1963 poration of Delaware Filed Dec. 1, 1960, Ser. No. 72,963 6 Claims. (Cl. 67-31) This invention relates to the manufacture of photoflash lamps and more particularly to the manufacture of photoflash lamps employing shredded zirconium f oil as the combustible.

Over the years, most of the commercial photoflash lamps, particularly those used by amateur photographers, have used shredded aluminum foil as the combustible and oxygen at pressures below atmospheric as the combustion supporting gas. In the manufacture of these lamps, it has been known that the time for the light output to reach its peak intensity may be readily controlled by known adjustments in shred size and in the composition and quantity of the primer or ignition paste applied to the ends of the lead-in wires. Generally speaking, the primer or ignition paste for aluminum shredded foil type photoflash lamps comprises one or more readily ignitable metal powders such 'as zirconium and magnesium for example mixed together with various combinations of oxidizing agents such as sodium chlorate, potassium, perchlorate, magnesium peroxide and the like suspended in a solution of a suitable binder such as nitrocellulose in amylacetate. Control of the peak time in photoflash lamps employing shredded aluminum foil as the combustible usually is effected by varying the shred size, varying the relative quantities of the ingredients of the foregoing composition and/ or varying the quantity of the paste which is applied to the tips of the lead-in wires of the flash lamps. For example, it is known that larger amounts of ignition paste give faster ignition and smaller amounts give slower peak times. It is also known that iaster ignition is obtained with finer shreds.

Recently, there has been made available commercially phototlash lamps in which the combustible is shredded zirconium foil, the combustion supporting gas is at a pressures substantially above atmospheric and the volume of the lamp envelope is substantially less than used heretofore. It has been found that the peak time of these lamps is reached much sooner than is desirable when conventional primer compositions heretofore used 'with aluminum filled lamps are used. Efforts to retard the peak time of these lamps by applying the techniques heretofore used in connection with aluminum filled lamps were not successful, although it would have been expected that the peak time could have been retarded successfully by the use of a very small amount of primer having very low oxidizing agent content. It has been found that many times these high pressure, zirconium filled flash lamps of very small volume will flash when very little or even no primer is used and the peak time still occurs much too soon for many practical uses for this type of lamp. When little or no primer is used the reliability of the ignition is rather erratic and an abnormally high percentage of the lamps do not flash at all.

In view of the foregoing, the principal object of this invention is to provide a reliable means for regulating and controlling, with a high degree of reliability, the peak time of photoflash lamps employing shredded zirconium foil as the combustible in an envelope with a high shred density and having a filling of combustion supporting gas at pressures substantially above atmospheric. Phis is accomplished by the use of a compatible plasticizer in the organic readily combustible binder employed in the primer paste composition.

In the accompanying drawing the photofl-ash lamp illustrated therein comprises a sealed light-transmitting envelope 11 within which a quantity of shredded zirconium foil 3 is disposed. The envelope 1 is provided with a filling of combustion-supporting gas, such as oxygen for example at a pressure of several atmospheres. A tungsten filament 5 is disposed within the envelope 1 and is attached to lead-in wires 7 and 9 which are supported by and extend through insulator button 8. The inner ends of the lead-in wires 7 and 9 are provided with a quantity of ignition paste 11. The lead-in wires 7 and 9 extend through an end of the lamp envelope and are bent into the form of stirrups 13 and 15 lying along opposite sides of the press 17, the wires finally re-entering the press 17 some distance away from the points at which they emerge. The stirrups 13 and 15 define electrical contact members for engagement with electrical contact members of a flashgun.

The lamp illustrated in the drawing, known commercial- 1y as an AG-l lamp, is substantially smaller in size than photoflash lamps heretofore available commercially. The lamp envelope 1 has a volume of about 1.2 cc. whereas the volume of photoflash lamps identified commercially as M2s, M5s and M25s for example is about 7.5 cc. Not only is the lamp envelope 1 considerably smaller in size than these commercial types of photoflash lamps but the shred density of the combustible is substantially greater. For example, the shred density of an M25 lamp is about 6 mg. per cc. lamp volume whereas the shred density of the illustrated AG-l lamp is about 18 mg. per cc. lamp volume. It is believed that the very close packing of the shredded foil influences the performance of the primer paste in such a way that the primer paste is inetfective as a means for obtaining peak time control if composed in the manner heretofore taught in the prior art.

In the fias-hlamp art, the time which el-apses from the closing of the electrical circuit to the first indication of light is called the dark time of the stem flash. The peak time of the lamp flash is the time which elapses from the closing of the electrical circuit to the time the light reaches its maximum intensity. In the case of the flashlamps of the type illustrated in the drawing and described above, the peak time With very small amounts of primer having a low oxidizing agent content or no primer at all was substantially the same, 9-12 msecs., and the reliability of ignition was not commercially acceptable. The desired peak time with a high degree of reliability is about 15 msecs.

We have found that a dark time of about 1.5 to 3.5 msecs. and a peak time of about 15 msecs., with a high degree of reliability, can be obtained by incorporating a plasticizer into the binder solution. The plasticizer apparently produces a delay in the ignition of the primer paste, thus increasing the length of the dark time and delaying the peak time. A surprising feature of this formulation is that when used with aluminum foil lamps, such as the Press 25 for example, it had no eltect on the peak time. The addition of 10%, 25% and 50% of a dioctylphthalate plasticizer, based on the amount of the nitrocellulose in the binder solution, did not cause any significant change in the peak time of an aluminum filled Press 25.

The advantageous effect which the introduction of a plasticizer into the primer paste has on delaying peak time in zirconium filled flashlamps is shown in the examples set forth below.

Example I.A primer paste batch comprising a mixture of 53.8 grams of zirconium, 23.1 grams of 200 mesh magnesium and 23.1 grams of potassium perchlorate suspended in 44.5 grams of a binder solution which in turn comprises 2.35 grams of 5 sec. R.S. nitrocellulose and 0.85 gram Flexol DOP in amylacetate.

Example II.-The composition of this rimer paste a batch is the same as in Example 1 except that Flexol 4G0 was used as the plasticizer instead of Flexol DOP.

Example IIl.-The composition of this primer paste batch is the same as in Example I except that Paraplex RG-2 was used as the plasticizer instead of Flexol DOP.

Photoflash lamps of the type illustrated in the accompanying drawing and described above were tested employing the various primer compositions set *forth in the foregoing examples and it was found that their average peak time was between 15 and 18 msecs, as compared to the 9-12 m'secs. peak time obtained when no plasticizer was employed in the primer paste composition.

Flexol is a trade name used by Carbide and Carbon Chemicals Co. for non-volatile plasticizers having a high boiling point. Flexol DOP is di-Z-ethylhexyl phthalate. Flexol 460 is polyethylene glycol di-Z-ethylhexoate. Paraplex RG2 is a flexible oil-modified sebacic acid type plasticizer resin manufactured by Rohm and Haas.

Other plasticizers which have been found to give satis factory results in delaying peak time are Cellufiex CEF and Santicizer M-17. The former is an organic phosphate ester, tris-b-chlorethyl phosphate, manufactured by Cela-.

nese Corporation. The latter is methyl phthalyl ethyl glycolate manufactured by the Monsanto Chemical Company.

From the foregoing examples it will be readily apparent to those skilled in the art that the addition of a plasticizer to the binder of the ignition paste provides an effective means for retarding the peak time of photoflash lamps having a high shred density of zirconium foil. It will also be appreciated that variations in primer composition from the specific compositions set forth in the foregoing examples may be made without departing from the spirit and scope of our invention. These variations will depend primarily on the length of dark time required to obtain the desired peak time. The primer compositions set forth above have been found to give good results where a dark time of about 1.5 to 3.5 msecs. is desired with lamps having a zirconium foil shred density of about 18 mgs./ ml. of lamp volume and in which the zirconium foil is about 1 mil by 2 mils in cross section. If the shred density is substantially less than about about 18 mgs/ml. of lamp volume, less plasticizer will be required to obtain the same control of peak time of the lamp; if the shred density is substantially greater than about 18 migs/ m1. of lamp volume, more plasticizer will be required to obtain the same peak time of the lamp at about 15 msecs. If longer peak times of the lamp than 15 msecs. are desired, with a shred density of about 18 mgs./ml. of lamp volume, a greater concentration of plasticizer would also be required.

We have found it preferable, in working with high shred density photofiash lamps employing shredded zirconium foil as the combustible, to hold the zirconium fill weight constant and adjust the shred width and primer composition to obtain the desired peak time. With respect to shred cross-section, it is known that generally speaking the smaller the cross-section the faster the peak time occurs. As a practical matter the foil thickness is usually held at about 1 mil and the width is adjusted between about 1 and 2 mils. With respect to the inorganic materials in the primer, not more than 50 to 60 parts by weight of zirconium metal powder should be used, along with about 5-25 parts by weight of magnesium and enough of an oxidizing agent such as potassium perchlorate to give parts by Weight of total inorganic components. The binder comprises R.S. type nitrocellulose of /2 to 5 sec. viscosity and a nitrocellulose plasticizer highly compatible therewith in a solvent such as :arnylacetate. The ratio of nitrocellulose, or other organic readily combustible binders such as ethyl cellulose for example, to the plasticizer is preferably in the range of from about 1:1 to 3:1. The dry ignition paste should contain from about 3 to 10 grams of organic material/ 100 grams of inorganic material. These primer paste compositions will give peak times in the range of about 13 to 18 msecs. in lamps of the type described.

What we claim is:

1. A primer composition for photoflash lamps comprising a powder mixture of readily ignitable metal and an oxidizing agent suspended in a solution of an organic readily combustible binder and a combustion-retarding plasticizer compatible therewith.

2. A primer composition for photofiash lamps comprising a powder mixture of zirconium and potassium perchlorate in a solution of an organic readily combustible binder and a combustion-retarding plasticizer compatible therewith.

3. A primer composition for photoflash lamps comprising a powder mixture of zirconium, magnesium and potassium perchlorate in a solution of an organic readily combustible binder and a combustion-retarding plasticizer compatible therewith.

4. A primer composition for photoflash lamps comprising a powder mixture of zirconium, magnesium and potassium perchlorate in a solution of nitrocellulose and a combustion-retarding plasticizer compatible therewith.

5. A flash l-amp comprising: a sealed light-transmitting envelope; a combustion-supporting gas fill-ing in said envelope; a quantity of filamentary zirconium closely packed in said envelope; and ignition means disposed in said envelope in operative relationship with respect to said filamentary zirconium, said ignition means including a primer composition containing an organic readily combustible binder and a combustion-retarding plasticizer compatible therewith.

6. A flash lamp comprising: a sealed light-transmitting envelope; a combustion-supporting gas filling in said envelope; a quantity of filamentary zirconium closely packed in said envelope; and ignition means disposed in said envelope in operative relationship with respect to said filamentary zirconium, said ignition means including a primer composition containing nitrocellulose and a combustion-retarding plasticizer compatible therewith.

References Cited in the file of this patent UNITED STATES PATENTS 1,935,495 Young Nov. 14, 1933 2,178,430 Mackie Oct. 31, 1939 2,263,179 Lockwood Nov. 18, 1940 2,487,906 Trevorrow Nov. 15, 1949 2,791,114 Cressman May 7, 1957 2,857,752 Anderson et al. Oct. 28, 1958 2,982,119 Anderson May 2. 196 

1. A PRIMER COMPOSITION FOR PHOTOFLASH LAMPS COMPRISING A POWDER MIXTURE OF READILY IGNITABLE METAL AND AN OXIDIZING AGENT SUSPENDED IN A SOLUTION OF AN ORGANIC 